Flowable fibre-reinforced concrete: Progress in understanding and development of design standards

Significant progress has been achieved during the past years in the understanding of the behaviour of fibres in flowable concrete clearly indicating the link between mix design, casting conditions and structural behaviour. With mix-designs deviating more or less from conventional vibrated concrete (CVC), constitutive laws and code provisions related to the structural behaviour, as established so far, might no longer be applicable. Transferring the research-garnered knowledge into design prescriptions is an effort made by fib Task Group 4.3. ModelCode 2010 has introduced the K-factor concept, a factor that takes into account fibre orientation to consistently identify the mechanical properties of the material to be employed for structural design. The current design approach is determining the highest K-factor of a structure by experimental testing to assure a safe design. Flow simulations can assist in the design and adequate test methods have been developed to assure the required quality level. This paper compiles recent research findings with regard to the flow behaviour and the standardisation of flowable fibre-reinforced concrete, a concrete type with a very high potential for production efficiency and the development of innovative products and structural applications. The synergy between tailored mixture composition, structural design methodologies and effective manufacturing/casting processes at a high level of quality is a strong engineering need to remain competitive and to fully exploit the potential that this category of advanced cement-based materials has for the construction industry.